splice_linux.go

     1  // Copyright 2018 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package net
     6  
     7  import (
     8  	"internal/poll"
     9  	"io"
    10  )
    11  
    12  // splice transfers data from r to c using the splice system call to minimize
    13  // copies from and to userspace. c must be a TCP connection. Currently, splice
    14  // is only enabled if r is a TCP or a stream-oriented Unix connection.
    15  //
    16  // If splice returns handled == false, it has performed no work.
    17  func splice(c *netFD, r io.Reader) (written int64, err error, handled bool) {
    18  	var remain int64 = 1 << 62 // by default, copy until EOF
    19  	lr, ok := r.(*io.LimitedReader)
    20  	if ok {
    21  		remain, r = lr.N, lr.R
    22  		if remain <= 0 {
    23  			return 0, nil, true
    24  		}
    25  	}
    26  
    27  	var s *netFD
    28  	if tc, ok := r.(*TCPConn); ok {
    29  		s = tc.fd
    30  	} else if uc, ok := r.(*UnixConn); ok {
    31  		if uc.fd.net != "unix" {
    32  			return 0, nil, false
    33  		}
    34  		s = uc.fd
    35  	} else {
    36  		return 0, nil, false
    37  	}
    38  
    39  	written, handled, sc, err := poll.Splice(&c.pfd, &s.pfd, remain)
    40  	if lr != nil {
    41  		lr.N -= written
    42  	}
    43  	return written, wrapSyscallError(sc, err), handled
    44  }
    45
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